Oral health outcomes and shift working among male workers: A cross-sectional survey

Working time outside routine daily working hours is known as shift working. Studies have shown adverse effects of shift working such as stress, obesity, and diabetes on the workers’ health. The aim of the present study was to compare aspects of oral health in shift workers and non-shift workers of a cement factory in Shahroud, Iran. Study population comprised of 180 male workers of the factory in the year 2015. Convenience sampling was continued until recruiting 180 subjects of shift- and non-shift workers. Data collection included oral health questionnaire, health and safety executive (HSE) questionnaire, and clinical oral examination. The Chi-square test, Pearson correlation coefficient, and generalized Poisson model were employed for statistical evaluation. Mean age of the workers was 39.19 (±9.48); 53% had educational level of less than diploma. Their mean DMFT was 12.89 (±5.75) which correlated with number of years in shift work schedule (Pearson correlation coefficient: 0.41; p<0.001) but not correlated with job stress (Pearson correlation coefficient: -0.11; p = 0.12). Mean number of deep periodontal pockets among the workers was 5.03 (±1.84) that showed correlation with number of years in shift work schedule (Pearson correlation coefficient: 0.33; p<0.001) but no correlation with job stress (Pearson correlation coefficient: -0.03; p = 0.68). Adherence to various oral health behaviors was reported by less than half of the workers. Positive correlation of dental caries and periodontal diseases with shift working partly signals negative impact of working conditions on oral health among this group of workers which calls for modifications in their working environment to facilitate health practices.

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Unfunded studies
Enter: The author(s) received no specific funding for this work.   (1). Special attention has been paid to the relationship between working hours and the amount of job stress with individuals' health. There is a direct relationship between working hours and damage to health (2). In addition to the amount, the distribution of working hours also affects health. The effect of shift work schedule on health has been documented (3).
Studies have shown relationship between working in different shifts with several unhealthy conditions such as diabetes (4), cardio-vascular diseases(5), obesity (6), and metabolic syndrome (7). Job stress is another factor that affects health both physically and mentally (8).
Occupation can affect oral health through stress or systemic illnesses caused by overwork (9, 9.5). Scalco et al. assessing oral health of 3253 office workers reported that overwork was associated with poorer oral health status and restricted individuals from adherence to oral healthrelated behaviors (10). Youshino et al. found that frequent stomatitis, gingival swelling and recession, unusual feeling in the mouth, bad breath, clicking sound in the jaw, and worn down teeth were associated with job stress among a group of workers in Japan (11). In Iran, studies regarding the relationship between work conditions and oral health status of workers are, 4 however, limited. The aim of this study was to evaluate the working conditions including shift work schedule and job stress on oral health in a group of workers of Shahroud Cement Factory.

Methods
The target population for this cross-sectional study was 180 male workers of Shahroud Cement Job stress questions.
The first section of the questionnaire was prepared in simple language and in accordance with the level of knowledge of the studied workers and was finalized after evaluating its validity and Reliability. To determine the validity, the questionnaire was given to 15 workers. After completing the questionnaire, they reported that the questionnaire was simple to understand, appropriate with no ambiguity or inadequacy in the meanings of the words. In order to determine the reliability of the questionnaire, the test-retest method was used. The questionnaire completed by 15 workers two times with two weeks interval. The reliability coefficient obtained at this stage was 0.7, which is in an acceptable range. Clinical oral examination included measuring periodontal pocket depth and DMFT index based on the WHO method for oral health survey (14) which was performed by one of the authors (RD). Periodontal pocket with >4 mm depth was regarded as sign of periodontal disease.
The Chi-square test, Pearson correlation coefficient, and generalized Poisson model served as statistical evaluation.

Results
The workers' mean age was 39.19 (±9.48) with average 13.91 (±7.24) years of work experience and 64% reported <10 years in shift work schedule. As it appears in Table 1, majority of the workers reported that working in the cement factory is their only job and for more than half of the workers, education level was below diploma and high perceived job stress.  Table 2 shows distribution of the workers' oral health-related behaviors and aspects of oral health -related quality of life according to their shift work pattern. The respondents' adherence to the oral health-related behaviors was as follows: at least twice per day toothbrushing by 9% (at least once per day by 18%), using dental floss at least once per day by 1%, eating or drinking sugary foods at least once per day by 42%, and having a dental visit in the past year by 33%.
More than 80% of the respondents reported that they had rarely or never pain, difficulty in communication, and difficulty in eating due to dental problems in the past three months. 8 As it appears in table 2, those workers with <10 years of shift work schedule reported higher frequency of at least twice per day toothbrushing (p=0.05), less frequency regarding difficulty in communication (p<0.001), and eating (p=0.02) due to dental problems in the past three months.
Having a dental visit in the past year was more prevalent among the workers with ≥10 years in shift work schedule.

Discussion
Findings of the present study failed to show a relationship between job stress with shift work schedule and oral health outcomes among the workers. A weak correlation, however, was found between shift work schedule and oral health outcomes. Favorable level of oral health behaviors among the workers was very infrequent especially for the use of dental floss and toothbrushing.
Psychological stress in result of working condition has been suggested as a risk factor for dental caries and periodontal diseases. One of the probable mechanisms in this regard is the effect of psychological stress on the individual's oral health behaviors (15). Among the workers in the 11 present study, work-related stress showed relationship neither with measures of dental caries and periodontal disease, nor with oral health related behaviors. Studies on the relationship between job stress and measures of oral health, however, show some sort of controversy. While some studies found that higher level of work stress is associated with poor oral health related quality of life (16) (11)., and less favorable level of oral health related behaviors (17), a systematic review found no evidence on the association of work stress with dental caries and tooth loss but some potential association between periodontal disease and work stress (18).
Being in the shift schedule for a long time correlated with less favorable oral health status among the workers in the present study in a way that those workers with more years in shift schedule experienced higher level of dental caries, periodontal diseases, and more difficulty in communication and eating due to dental problems. This finding is in line with studies showing the association of non-standard work schedules with less favorable health outcomes (19) (20,21). Non-standard working schedule is proposed as a trigger for physiological changes resulting to disturbances in sleep pattern and circadian rhythms and ultimately reduce the workers' adaptive capabilities (22). To the best of our knowledge this study seems to be the first in quest for a relationship between shift working schedule and oral health outcomes. On the other hand, the relationship between various working time characteristics with employees' health status has been studied largely. For example, young adult American workers without a regular day shift pattern of working showed higher risk for a wide range of health-related outcomes comparing to workers with standard regular daytime schedule (20). Irregular work schedule found to have negative impact on quality of sleep and sense of coherence among a group of Hungarian nurses (21). Due to the importance of oral health on the quality of life and productivity of the workers, incorporating the oral health indicators into the comprehensive studies of the workers' health is called for.
Adherence to healthy behaviors is an essential prerequisite for good oral health status. Very little percentage of the participants in this study, however, reported complying with toothbrushing at least twice per day and using dental floss. Having a dental visit and restricting the sugary food were also a rare finding since about two third of the workers did not report a dental visit and close to 60% reported more than once per day eating sugary foods. This may be a reflection of either underestimation of the importance of best oral hygiene practices by those workers or their difficult working condition that hinder them from performing recommended level of oral health behaviors. Data on the oral health of the workers in Iran is rare. However, findings of a recent study on a group of employees in Tehran (23), show higher prevalence for toothbrushing (28%), using dental floss (48%), and dental visit (77%) compared to the present study. Another study from Mashhad city (24), that included employees as participants, found that at least 34% brush their teeth twice per day and 35% use dental floss in a daily basis. Different figures of the prevalence of oral health behaviors reflect underestimation of the importance of recommended criteria for favorable level of oral health and also different level of socio-economic status and cultural diversity of the participants in the previous studies. Reaching to higher rates of favorable level of oral health behaviors among working age population is not a dream since findings of some studies from foreign countries show promising results in this regards. For example, toothbrushing on at least 2/day basis has been reported by more than 90% of a group of Korean workers (25) and around 80% of a representative sample of adult population from eight European countries (26). 13 Findings of this study should be interpreted with caution due to some limitations. First is the inherent limitation of cross-sectional study which cannot make a causal inference between variables. Second is the convenient sampling which makes the generalization of the findings to the whole population uncertain. Third is the limitation of questionnaire surveys which is prone to socially acceptable answers and recall bias.

Conclusion
Correlation of shift working with dental caries and periodontal diseases among the workers in this study speaks for a potential risk for oral health of workers. Provision of rather stable working time would help workers for better adherence to optimal oral health behaviors which in turn enhance their overall health status and productivity.